The present disclosure relates to an image sensor and a method of manufacturing the same. In more detail, the present disclosure relates to a complementary metal-oxide-semiconductor (CMOS) image sensor having an improved sensitivity and a method of manufacturing the same.
In general, an image sensor is a semiconductor device that converts an optical image into electrical signals, and may be classified or categorized as a charge coupled device (CCD) or a CMOS image sensor (CIS).
The CMOS image sensor includes unit pixels, each including a photodiode and MOS transistors. The CMOS image sensor sequentially detects the electrical signals of the unit pixels using a switching method, thereby forming an image.
The CMOS image sensor is made by forming photodiodes in or on a semiconductor substrate, forming transistors connected to the photodiodes on the semiconductor substrate, forming wiring layers functioning as signal lines connected to the transistors, and forming a color filter layer and micro lenses on or over the wiring layers.
Especially, the CMOS image sensor includes a plurality of pixel regions arranged in rows and columns, and a photodiode, a transfer gate, a floating diffusion region, etc. are formed in or on each pixel region. For example, the photodiode includes a p-type surface layer and an n-type storage region, and when incident light strikes the surface of the photodiode, electrons (charge carriers) are generated in the depletion region of the p-n junction of the photodiode. The electrons are accumulated in the n-type storage region, and then moved to the floating diffusion region through the transfer gate.
The sensitivity of the image sensor may be determined by the quantity of electric charge accumulated in the photodiode. However, as the degree of integration of the image sensor is increased, the size of the photodiode is decreased, and the sensitivity of the image sensor may thus be deteriorated.